Why, moreover, does this line always start in the centre of the sticky network and nowhere else? Because that is the point where the spokes meet and, therefore, the common centre of vibration. Anything that moves upon the web sets it shaking. All then that is needed is a thread issuing from this central point to convey to a distance the news of a prey struggling in some part or other of the net. The slanting cord, extending outside the plane of the web, is more than a foot-bridge: it is, above all, a signalling-apparatus, a telegraph-wire.
Let us try experiment. I place a Locust on the network. Caught in the sticky toils, he plunges about. Forthwith, the Spider issues impetuously from her hut, comes down the foot-bridge, makes a rush for the Locust, wraps him up and operates on him according to rule. Soon after, she hoists him, fastened by a line to her spinneret, and drags him to her hiding-place, where a long banquet will be held. So far, nothing new: things happen as usual.
I leave the Spider to mind her own affairs for some days, before I interfere with her. I again propose to give her a Locust; but, this time, I first cut the signalling-thread with a touch of the scissors, without shaking any part of the edifice. The game is then laid on the web. Complete success: the entangled insect struggles, sets the net quivering; the Spider, on her side, does not stir, as though heedless of events.
The idea might occur to one that, in this business, the Epeira stays motionless in her cabin since she is prevented from hurrying down, because the foot-bridge is broken. Let us undeceive ourselves: for one road open to her there are a hundred, all ready to bring her to the place where her presence is now required. The network is fastened to the branches by a host of lines, all of them very easy to cross. Well, the Epeira embarks upon none of them, but remains moveless and self-absorbed.
Why? Because her telegraph, being out of order, no longer tells her of the shaking of the web. The captured prey is too far off for her to see it; she is all unwitting. A good hour passes, with the Locust still kicking, the Spider impassive, myself watching. Nevertheless, in the end, the Epeira wakes up: no longer feeling the signalling-thread, broken by my scissors, as taut as usual under her legs, she comes to look into the state of things. The web is reached, without the least difficulty, by one of the lines of the framework, the first that offers. The Locust is then perceived and forthwith enswathed, after which the signalling-thread is remade, taking the place of the one which I have broken. Along this road the Spider goes home, dragging her prey behind her.
My neighbour, the mighty Angular Epeira, with her telegraph-wire nine feet long, has even better things in store for me. One morning, I find her web, which is now deserted, almost intact, a proof that the night’s hunting has not been good. The animal must be hungry. With a piece of game for a bait, I hope to bring her down from her lofty retreat.
I entangle in the web a rare morsel, a Dragon-fly, who struggles desperately and sets the whole net a-shaking. The other, up above, leaves her lurking-place amid the cypress-foliage, strides swiftly down along her telegraph-wire, comes to the Dragon-fly, trusses her and at once climbs home again by the same road, with her prize dangling at her heels by a thread. The final sacrifice will take place in the quiet of the leafy sanctuary.
A few days later, I renew my experiment under the same conditions, but, this time, I first cut the signalling-thread. In vain I select a large Dragon-fly, a very restless prisoner; in vain I exert my patience: the Spider does not come down all day. Her telegraph being broken, she receives no notice of what is happening nine feet below. The entangled morsel remains where it lies, not despised, but unknown. At nightfall, the Epeira leaves her cabin, passes over the ruins of her web, finds the Dragon-fly and eats her on the spot, after which the net is renewed.
One of the Epeirae whom I have had the opportunity of examining simplifies the system, while retaining the essential mechanism of a transmission-thread. This is the Crater Epeira (Epeira cratera, WALCK.), a species seen in spring, at which time she indulges especially in the chase of the Domestic Bee, upon the flowering rosemaries. At the leafy end of a branch, she builds a sort of silken shell, the shape and size of an acorn-cup. This is where she sits, with her paunch contained in the round cavity and her forelegs resting on the ledge, ready to leap. The lazy creature loves this position and rarely stations herself head downwards on the web, as do the others. Cosily ensconced in the hollow of her cup, she awaits the approaching game.
Her web, which is vertical, as is the rule among the Epeirae, is of a fair size and always very near the bowl wherein the Spider takes her ease. Moreover, it touches the bowl by means of an angular extension; and the angle always contains one spoke which the Epeira, seated, so to speak, in her crater, has constantly under her legs. This spoke, springing from the common focus of the vibrations from all parts of the network, is eminently fitted to keep the Spider informed of whatsoever happens. It has a double office: it forms part of the Catherine-wheel supporting the lime-threads and it warns the Epeira by its vibrations. A special thread is here superfluous.